The present invention relates to flywheels employed in the drivetrain of vehicles, and more particularly to dual mass flywheels.
Conventional vehicle drivetrains regularly employ a flywheel between a vehicle engine and clutch in order to reduce the engine pulsations from propagating throughout the vehicle driveline. When the clutch is engaged, the flywheel also helps to improve noise, vibration and harshness (NVH) characteristics for the transmission as well. However, with the smaller engines that are now being used and the ever increasing demands to improve vehicle NVH characteristics, the single mass flywheel has proven to be inadequate to address these NVH concerns for both the engine and the transmission. One of the reasons for this is that a smaller engine, such as a three or four cylinder engine, generally requires a higher relative inertia in order to achieve effective vibration isolation than does a larger engine, such as a six or eight cylinder engine.
As a result, some have employed dual mass flywheels connected to the engine and the clutch. While these types of flywheels generally improve the transmission NVH, they generally reduce the effectiveness of the flywheel in improving the NVH of the engine. In these dual mass flywheels, a primary flywheel mass is connected directly to the engine crankshaft, while a secondary mass is connected to the primary mass via a spring and damper assembly. The primary flywheel mass has lower inertia than that of a conventional flywheel, and so is less effective in reducing transmission of the engine pulsations since the pulsations are reduced only by the inertia connected directly to the engine crankshaft. This increase in the engine NVH can lead to increased wear on the crankshaft or damage to accessories driven off of the front end accessory drive. As a result, those employing dual mass flywheels end up adding additional damper assemblies and friction plates to account for the engine NVH concerns.
Further, with the smaller engines, there is a also desire to reduce the engine rotating inertia in order to improve the vehicle launch. Thus, it is desirable to have a vehicle driveline that overcomes the drawbacks of current vehicle drivelines. In particular, it is desirable to have a flywheel and clutch assembly that will adequately reduce the NVH characteristics from both the engine and transmission, while also allowing for improved vehicle launch.
In its embodiments, the present invention contemplates a flywheel and clutch assembly for transferring torque from an engine crankshaft to a transmission input shaft. The assembly includes a primary mass adapted to be rotationally fixed to the engine crankshaft, a clutch disc adapted to be rotationally fixed to the transmission input shaft, and a secondary mass rotationally engageable with the clutch disc for transferring torque thereto. A spring assembly is coupled between the primary mass and the secondary mass, and a latcher is connected between the primary mass and the secondary mass that is engageable to rotationally fix the primary mass to the secondary mass.
According to an embodiment of the invention, it has a variable inertia flywheel where a primary mass and a secondary mass can be coupled together via a spring or a spring and damper assembly under certain vehicle driving conditions, but can also be latched together to rotate as one mass under other vehicle driving conditions.
An advantage of an embodiment of the present invention is that the flywheel and clutch assembly will adequately reduce the NVH for both the engine and the transmission.
Another advantage of an embodiment of the present invention is that the vehicle will have improved vehicle launch characteristics.
A further advantage of an embodiment of the present invention is that a mechanism employed to latch a primary and secondary mass together under certain driving conditions can also operate as a variable damper between the primary and secondary masses under other driving conditions.